In recent years a number of minimally invasive techniques have been developed to treat occlusive vascular disease, and to repair aneurysms occurring in organs and vessels.
In occlusive vascular disease, such as arteriosclerosis, plaque accumulates within a vessel and gradually narrows the vessel to the degree that the vessel can no longer supply an adequate flow of blood. A number of vascular prostheses have been developed to re-expand and retain the patency of such afflicted vessels, for example, after atherectomy or angioplasty. U.S. Pat. No. 4,733,665 to Palmaz describes one type of balloon-expandable stent structure to treat occlusive disease.
It is often desirable to support a tortuous vessel, or one having a diameter that changes along the length of the vessel. U.S. Pat. No. 5,421,955 to Lau et al. describes a stent comprising a series of linked sinusoidal rings. That patent describes that the individual sinusoidal elements may be differentially expanded to accommodate diameter changes in the vessel.
A drawback of the foregoing previously known devices, however, is that such devices are not readily deployable in bifurcated vessels, so that one portion of the stent may be deployed in a trunk vessel having a large diameter, and a second portion of the stent may be deployed in a branch vessel having a much smaller diameter. Moreover, because branch vessels often form an angle with trunk vessels, previously known devices cannot be readily employed in such environments.
With respect to treatment of aneurysms, previously known minimally techniques generally seek to "re-line" a flow path through the organ, for example, by fixing a graft across the weakened tissue of the aneurysm. The graft is then held in place with one or more stents, which may be implanted, for example, using a balloon catheter. Such arrangements are described, for example, in Parodi U.S. Pat. No. 5,219,355, European Application No. 0 461 791, and Clouse U.S. Pat. No. 5,211,658.
A number of techniques also have been developed for deploying graft systems in bifurcated anatomy, such as the aorto-iliac bifurcation. For example, U.S. Pat. No. 4,562,596 to Kornberg describes a graft comprising a main portion having first and second legs extending therefrom. The main portion is deployed in the aorta, while the first and second legs are deployed in the iliac arteries. U.S. Pat. No. 5,360,443 to Barone et al. and U.S. Pat. No. 5,489,295 to Piplani et al. describe similar devices.
Other bifurcated graft systems, as described in U.S. Pat. Nos. 5,575,817 to Martin and 5,609,627 to Goicoechea et al., so called "asymmetric grafts," comprise a main portion having a long first leg, and a much shorter second leg. The grafts are deployed so that the long leg is disposed in the iliac artery used to gain access to the aorta, and so that the short leg does not extend into the contralateral iliac artery. In a separate step, an extension portion is then attached to the short leg, thus extending the second leg into the contralateral artery.
In view of the foregoing, it would be desirable to provide a stent having first and second portions that may be deployed to different expanded diameters.
It would further be desirable to provide a stent capable of being deployed in a bifurcated vessel that enables a first portion of the stent to be deployed in a trunk vessel having a first longitudinal axis, and a second portion of the stent to be deployed in a branch vessel having a second longitudinal axis, the second longitudinal axis forming an angle with the first longitudinal axis.
It would be still further desirable to provide a stent structure suitable for use as a support element of a bifurcated graft system.
It would be yet further desirable to provide methods of constructing and deploying a stent-graft system that overcome drawbacks of previously known stent and stent-graft systems.